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\chapter*{Abstract}
With the standardization of the 802.11 technology, wireless networks have
become more and more popular for Internet access. Besides expensive commercial
hotspots, there  are also a lot of Wi-Fi sharing communities operated by 
hobbyists  for sharing their bandwidth with
others. Some
of them have even been adopted as business model by
commercial companies like FON. 

As the world wide largest Wi-Fi sharing community, FON provides their
members free Internet access everywhere and in return the members share
part of their bandwidth with other people. 
FON's business model is based on
the sale of Internet access tickets for non-community members.

However this sharing model for wireless network still has many unsolved problems.
The authentication and user access control are not secure enough, the
transmission is done in plain text and the operator of the access point 
may be held responsible for all activities in association with his IP
address. Highly desired features like mobility are also not possible.

In this thesis, we present our peer-to-peer proposal for secure and
scalable Wi-Fi sharing by using the Host Identity Protocol (HIP) as building 
block. The HIP is an emerging technology which adds a new namespace, the
Host Identity namespace,  in the
current TCP/IP stack between IP and transport layer, thus it decouples the
dual role of the IP address. Applications will be bound to the Host
Identity instead of the IP address. In this way mobility and multihoming
will be possible. The transmission is protected by IPsec ESP. In our
approach, 
we delegate security and other features
to HIP and
integrate the user authentication
into HIP Base Exchange. The liability problem is solved in a way that we build a HIP tunnel
from the mobile user to the home router and from there to the Internet.

